The invention relates in general to cooling systems and in particular to apparatus and methods for evaluating the performance of cooling systems.
Cooling systems help prevent heat stress in humans exposed to extreme climates or work environments. A personal cooling system enables chilled fluid to circulate through tubing placed in garments worn by a person. In some personal cooling systems, the tubing on the person is tethered or connected to heavier components (for example, heat exchangers) that cool the fluid in the tubing. Thus, the heavier components, including power supplies and compressors, are not carried by the person being cooled. Vehicle-mounted personal cooling systems may be mounted in a vehicle, such as an air or ground vehicle, and connected to a person or persons in the vehicle via the fluid tubing. A Microclimate Cooling Unit (MCU) mounted in a vehicle may be used to chill fluid that provides cooling to a vehicle's crew via tubing in garments worn by the crew.
The performance of an MCU can degrade because of normal wear and tear, physical damage, or excessive use. A performance-degraded MCU uses more power and cools less than an MCU that is operating at standard or normal efficiency. In some environments, loss of cooling results causes only personal discomfort. However, in very high temperature environments, such as compartments of armored vehicles deployed in a desert and containing many heat-producing electronic devices, the loss of cooling in the compartment can result in severe heat sickness. Heat sickness adversely affects humans' decision-making abilities, which are critical to survival when engaged with hostile parties or when operating an air or land vehicle.
There exists no simple way to accurately test the performance of an MCU at its point of use. MCUs may be as small as about 6 inches by 6 inches by 14 inches with little space in the interior to access any of the refrigeration components for testing purposes. Also, the MCU housings are not easily opened at the point of use.
An MCU can be shipped from its point of use to another location, such as the manufacturer's facility, for testing with a laboratory testing system. The heat load used to test an MCU in a laboratory test system is generally a multi-gallon capacity heated water reservoir. The manufacturer's testing system is accurate, although it is not portable. The size and weight of the water reservoir and the power need to heat the water in the reservoir preclude ease of portability. So, the MCU must be shipped from its point of use to the laboratory testing system. This process is expensive and time-consuming because all MCUs, whether performance-degraded or not, must be sent to the manufacturer for testing.
An onsite temperature differential test can be used to provide some indication of MCU performance. The temperature differential test includes measuring surface temperature at two locations on a bottom surface of the MCU, using a hand-held infrared temperature sensor. If the difference in temperature between the two locations is greater than 10 degrees F., then the MCU is considered to be performing adequately. While better than no test at all, the temperature differential test does not provide a very accurate indication of the actual cooling performance of an MCU. No heat load is applied to the MCU using the temperature differential test. Thus, properly-performing MCUs may be misdiagnosed as performance-degraded and shipped away for further testing, and performance-degraded MCUs may be misdiagnosed as properly-performing and not shipped for further testing.
In the case of the U.S. Army, over 7,000 MCUs have been deployed in Army aviation and ground vehicles. It is costly and time-consuming to ship this large number of MCUs from their respective points of use to suitable locations for performance testing. A need exists for a more accurate performance testing apparatus that can be used at the point of use of an MCU.